1. Field of the Invention
The present invention relates generally to liquid fuel solutions of hydrocarbons and particularly to the storage of natural gas, primarily for vehicular use, in liquid solution with other hydrocarbons.
2. Description of Related Art
Composed essentially of methane, natural gas (NG) is an important competitor in the field of alternative fuels. NG is economic, and it offers a greater reduction in CO, NO.sub.x and non-methane hydrocarbon (NMHC) emissions. However, the on-board storage limitations of NG are a severe drawback to the use of NG as a vehicular fuel.
Conventional storage techniques for NG involve compression and liquefaction methods. The former is termed compressed natural gas (CNG) while the latter is known as liquefied natural gas (LNG). CNG requires bulky, high-pressure vessels to store a quantity of NG that delivers about one-sixth the range of an equal amount of gasoline under normal operating conditions. LNG provides nearly two-thirds the range of a comparable volume of gasoline, but requires cryogenic processing equipment and cryogenic storage.
In addition to the on-board storage problems of CNG and LNG, the logistics of the preparation and delivery of these fuels pose inconveniences. CNG at 21 MPa requires a delivery system operating above the storage pressure to ensure that a full charge is obtained. Therefore, a compression plant must be at or very near the vehicle refueling site.
LNG is liquified through a cryogenic procedure, and then delivered to a staging area before being dispensed to vehicles. This method requires a heavily insulated storage vessel to stage the fuel and a similarly insulated tank on board the vehicle.
In view of the drawbacks associated with CNG and LNG storage techniques, it is highly desirable to devise a safe, economical and convenient way to store NG for use as a vehicular fuel. A practical natural gas storage system should be characterized by (1) moderate storage pressures, so that high-pressure vessels like those required for storage of CNG are unnecessary; and (2) moderate storage temperatures, so that cryogenic equipment needed for storage of LNG is not a requirement.